1. Field of the Invention
This invention relates to a preumatic tire and particularly but not exclusively to a radial tire and provides a construction improved in materials usage and a manufacturing method improved in cost efficiency.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Conventional pneumatic tires have a reinforced carcass extending between two wheelrim contacting bead regions through sidewall regions and a ground contacting tread region. Inflation pressure within the cavity formed by mounting the tire onto the wheelrim tensions the carcass and thus provides the primary load support mechanism.
In a modern radial tire construction the carcass is reinforced by a ply of tire fabric comprising radially or substantially radially orientated cords which extend through the carcass continuously from one bead region to the other through the sidewalls and tread. These carcass cords are anchored in each bead region by being folded around an inextensible circumferentially extending bead core or hoop to form ply turn-up portions.
Furthermore in the tread region of the conventional radial tire the ground contacting rubber tread strip is also reinforced by a substantially inextensible belt or breaker taking the form of a cylindrical band. The belt or breaker is disposed radially outward and adjacent to the carcass ply and inward of the rubber tread strip and any tread pattern formed therein. This belt or breaker has substantially the same axial width as the tire tread and functions to keep the tread flat on the road surface. Breakers conventionally comprise plural plies of tire fabric having parallel cords which are inclined to the tire circumferential direction and crossed with respect to the cords of adjacent plies. Breaker plies may comprise organic cords or glass fibers but are usually steel coris.
In tires of the older so-called "crossply" construction the carcass comprises usually two or more plies having cords inclined to the tire circumferential direction and crossed with respect to the cords of adjacent carcass plies. Such crossply tires may also be fitted with breakers in the tread in a so-called `bias belted` tires.
Thus is became clear to the Inventor of the present application in studying general aspects of tire construction that a substantial proportion of tires have a surfeit of reinforcement in certain regions and particularly tires which benefit from the presence of a belt or breaker in the tread strip have a more than adequate level of total reinforcement in the tread region.